This invention pertains to electrical discharge machining, typically referred to "EDM", and more particularly to an apparatus and method for mounting an EDM electrode to an EDM machine.
Broadly, the EDM process employs an electrode which is brought into contact with a workpiece to form a cavity in the workpiece. The electrode is machined to provide an desired shape, corresponding to the final desired shape of the cavity. The EDM process is typically employed to manufacture tools and dies.
In the EDM process, setting up of the EDM electrode on the EDM machine is a critical step. The electrode must be properly positioned in the horizontal X and Y axes, as well as in the vertical Z axis. The electrode is typically mounted to an electrode holder, which includes a stem adapted to be received within a hydraulic quick clamp holder, which is then mounted to a chuck or the like. The electrode must be carefully positioned relative to the electrode holder, to ensure that the electrode is properly positioned relative to the EDM machine. In the past, this has been a time-consuming and difficult step in the setting-up process.
Various ways of mounting the electrode to the electrode holder are known. For instance, the electrode can be soldered to a flat end of the electrode holder, or the electrode may be provided with a recess adapted to receive the end of the holder, with the electrode being glued in place on the holder. Alternatively, a threaded opening can be formed in the electrode to receive a male threaded projection provided on the electrode holder, or horizontal passages formed in the electrode, through which threaded fasteners extend to fix the electrode to the electrode holder. One such arrangement provides a vertical flat surface against which a flat inner surface of the electrode is engaged, with bolts extending through the electrode and into threaded openings formed in the vertical flat surface of the electrode holder. While the last-described mounting arrangement provides positioning of the flat surface of the electrode in one horizontal direction, there is nothing in the prior art which discloses any means for positioning the electrode in the other horizontal direction when the electrode is being mounted to the electrode holder.
Accordingly, it is an object of the present invention to provide an electrode holder which is capable of properly positioning the electrode in both horizontal axes when the electrode is mounted to the holder. It is a further object of the invention to provide a system for positioning the electrode in both horizontal axes which is simple to carry out and which provides accurate and reliable positioning of the electrode on the holder. It is a further object of the invention to provide an arrangement for modifying the electrode to allow the electrode to interface with the electrode holder to provide accurate positioning of the electrode on the electrode holder along both horizontal axes.
In accordance with one aspect of the invention, the EDM electrode is provided with a substantially flat surface located toward its inner end, and an electrode holder includes an electrode-mounting block to which the electrode is adapted to be secured. The block includes a substantially vertical flat mounting surface adapted to engage the flat inner surface of the electrode. A mounting arrangement, such as a stem, is secured to the block for mounting the block to an EDM machine in a predetermined position along a longitudinal, or vertical, axis. A lateral positioning arrangement is interposed between the flat surface of the electrode and the flat vertical mounting surface of the block, for locating the electrode in a predetermined position along an axis transverse to the longitudinal axis and parallel to the flat vertical mounting surface of the block, and a connection arrangement is provided for connecting the electrode to the block. The flat vertical mounting surface of the block is located at a predetermined offset from the longitudinal axis, to allow the electrode to be located in a predetermined position along a second horizontal axis, perpendicular to the flat vertical mounting surface of the block. The lateral positioning arrangement includes one or more pins which extend outwardly from the flat vertical mounting surface of the block in a predetermined position relative to the longitudinal axis. One or more openings are formed in the electrode in predetermined positions toward its inner end, corresponding in location to the locations of the one or more pins. The pins are engageable within the openings when the flat surface of the electrode is engaged with the flat vertical mounting surface of the block, to position the electrode along an axis transverse to the longitudinal axis. In a preferred form, one of the pins is offset from the other of the pins in a direction along the longitudinal axis, and the openings in the electrode are in a corresponding pattern, to ensure that the proper surface of the inner end of the electrode is engaged with the flat mounting surface of the block.
In accordance with another aspect of the invention, a holder for an EDM electrode is constructed substantially in accordance with the foregoing summary.
The invention further contemplates a method of mounting an EDM electrode to an EDM electrode holder. The method involves the steps of providing a lateral positioning arrangement between the flat surface of the electrode and the flat mounting surface of the electrode holder, to locate the electrode in a predetermined position along an axis transverse to the longitudinal axis and parallel to the flat vertical mounting surface of the electrode holder, and securing the electrode to the electrode holder. The step of providing a lateral positioning arrangement is substantially as summarized previously, i.e. providing one or more pins which extend outwardly from the flat vertical mounting surface of the electrode holder, and one or more openings in the electrode engageable with the one or more pins. The step of forming one or more openings in the electrode is preferably carried out by maintaining the electrode in a predetermined position in a jig prior to mounting the electrode to the electrode holder. The jig has one or more passages in locations corresponding to the pattern of the one or more pins, and a boring tool is inserted through the passages in the jig to form the one or more openings which are adapted to receive the one or more pins. The jig is preferably constructed of two sections which cooperate to define a slot adapted to receive the electrode, with the sections being movable toward and away from each other between a clamping position and a release position. The electrode is placed in the slot when the jig sections are in their release position, and the sections are then moved to their clamping position to engage the electrode and to maintain it in position within the slot.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.